348 LIGHTING OILS sulphuric acid (D 1-53) and note made if the latter becomes yellow or brown. If any appreciable coloration occurs, it is desirable to ascertain if any marked rise of temperature takes place. 3. Determination of the Sulphur.—This is usually done only with oils having a penetrating and unpleasant odour. The simplest method is that of Heussler and Engler,1 this consisting in burning the petroleum in a suitable lamp, the chimney of which is joined to a bent tube dipping into 20 c.c. of 5% potassium hydroxide solution made just yellow by bromine and then left in the air to decolorise ; the absorption vessel communicates with a pump. The lamp charged with the oil is weighed and lighted, the tube fitted and the suction adjusted so that the combustion is complete and regular. The sulphurous anhydride produced is absorbed and transformed into sulphuric acid by the alkaline bromine solution. After 10-12 grams of the oil are burnt, the flame is extinguished, a little more air drawn through, the lamp again weighed and the sulphuric acid determined as barium sul- phate. The caustic potash used and also the air must, of course, be free from sulphur products. The sulphur may also be determined by the Mahler calorimetric bomb (see Crude Petroleum, Chemical Tests, 3). 4. Distinction between Petroleums from Different Localities.— This is based mainly on the following tests : (a) SPECIFIC GRAVITY. This is usually 0-780-0-805 for American and 0-820-0-825 for Russian lighting oils. A better criterion than the specific gravity is furnished by the specific gravities of the fractions obtained on distillation, these differing by about 0-04 for identical boiling points. Thus, the fractions of an American and a Russian petroleum distilling between 230° and 250° have the respective densities 0-798 and 0-841, and the fractions between 250° and 270° the densities 0-809 an-d 0-850. (6) TREATMENT WITH BROMINE. 2 or 3 c.c. of American petroleum are not coloured when treated with a drop of bromine, whereas other petroleums become coloured under these conditions. (c) SOLUBILITY IN A MIXTURE OF CHLOROFORM AND ALCOHOL. Riche and Halphen 2 have suggested a method based on the different solubilities, in a mixture of chloroform and aqueous alcohol, of fractions of equal specific gravities from American and Russian petroleums. It is carried out as follows : Several successive fractions of the oil are separated by distillation and the specific gravity of each of them determined at 15°. The volume of a mixture in equal volumes of pure anhydrous chloroform and 92-8% alcohol necessary, when run in slowly from a burette with continual shaking, to remove the turbidity produced, is then determined. For the lighter fractions (which have about the same compositions with Russian and American petroleums), the solubility is about the same for the same specific gravities, but for fractions with specific gravities above 0-760, the difference in solubility continuaUy increases. Thus, the corresponding fractions of 1 Chem. Zeit., 1896, p. 197. ,2 Journ. de Pharm. et Chim., 1894, XXX, p. 289 ; Rossi: Ann. Labor. Chim. Gabelle, 1900, IV, p. 379. substances in 20 c.c. of the oil.